Seismic Anisotropy Reveals Deep-Mantle Dynamics

Source: Geochemistry, Geophysics, Geosystems

In some components of Earth’s inside, seismic waves journey at completely different speeds relying on the route through which they’re shifting by the layers of rock in Earth’s interior. This property is named seismic anisotropy, and it may supply essential details about how the silicate rock of the mantle—significantly on the mantle’s lowermost depths—deforms. In distinction, areas by which seismic waves journey on the similar pace no matter route are thought of isotropic.

In the underside 300 kilometers of the mantle, often known as the D layer, anisotropy is doubtlessly attributable to mantle plumes or mantle circulation interacting with the perimeters of large low-shear-velocity provinces: continent-sized, dense, scorching BLOBs (massive lower-mantle basal constructions) on the base of the mantle above the core. Many questions persist concerning the viscosity, motion, stability, and form of the BLOBS, in addition to about how they are often influenced by mantle plumes and subduction.

Roy et al. used ASPECT, a 3D mantle convection modeling software program, and ECOMAN, a mantle cloth simulation code, to look at the deep mantle. They examined 5 completely different mantle mannequin configurations, adjusting the viscosity and density of the BLOBs. The purpose was to see which configuration would most carefully re-create the noticed seismic anisotropy.

The researchers handled the BLOBs as areas with their very own distinctive chemistry, which kind from a 100-kilometer-thick layer on the backside of the mantle. Their fashions simulated how mantle plumes shaped over the previous 250 million years, throughout which period occasions such because the breakup of Pangaea, the opening of the Atlantic, and the evolution of assorted subduction zones occurred.

The examine means that the perfect rationalization for noticed seismic anisotropy is when the BLOBs are 2% denser and 100 occasions extra viscous than the encircling mantle. This aligns with observations of anisotropy patterns in seismic information. Plumes kind primarily on the edges of BLOBs, the place robust deformation causes robust anisotropy. (Geochemistry, Geophysics, Geosystems, https://doi.org/10.1029/2025GC012510, 2025)

—Rebecca Owen (@beccapox.bsky.social), Science Writer

Citation: Owen, R. (2025), Seismic anisotropy reveals deep-mantle dynamics, Eos, 106, https://doi.org/10.1029/2025EO250392. Published on 21 October 2025.

Text © 2025. AGU. CC BY-NC-ND 3.0
Except the place in any other case famous, pictures are topic to copyright. Any reuse with out categorical permission from the copyright proprietor is prohibited.

Related